PROJECT SUMMARY Loss of the extracellular matrix (ECM) protein elastin leads to the uncontrolled proliferation of vascular smooth muscle cells (VSMCs). This proliferation is accompanied by a loss in contractility of VSMCs and in humans manifests as the condition supravalvular aortic stenosis (SVAS). SVAS patients experience progressive occlusion of their arterial lumen, ultimately leading to vessel stiffening and heart failure, for which the mechanisms remain largely unknown. Preliminary data has shown an upregulation of both chondroitin sulfate and the associated proteoglycan versican in the ascending aortas of elastin haploinsufficient mouse models, and both have been linked to impaired elastogenesis and hyperproliferation. Further, as signaling by integrin ?3 and FAK is upregulated in SVAS, while expression of smooth muscle contractile markers is reduced, I hypothesize that abnormal ECM composition under elastin haploinsufficiency is recognized and transduced by the internal VSMC environment, leading to a shift from a differentiated to a proliferative phenotype. I will assess this hypothesis using induced pluripotent stem cells (iPSCs) as a model platform, as iPSCs present a limitless supply of patient-specific cells unattainable through other conventional methods and complement my findings with an in vivo mouse model of SVAS. In Aim 1, I will phenotypically validate elastin haploinsufficient iPSC-derived VSMCs specific to the neural crest lineage to phenocopy SVAS and try to rescue the phenotype through interfering with versican assembly in vivo and in vitro. In Aim 2, I will study the biomechanical signal transduction involved in the phenotypic switching of elastin haploinsufficient VSMCs from a differentiated, contractile state to a dedifferentiated, proliferative state in both iPSC and mouse models of SVAS. These aims involve in vivo studies of murine models, immunofluorescence, western blotting, qPCR, 2D- and 3D-modeling using iPSCs. The objectives of these aims are to identify key factors in the uncontrolled proliferation observed by VSMCs under elastin haploinsufficiency, and methods of rescuing this defect. This proposal addresses important, understudied mechanisms of vascular proliferation, and has the potential to facilitate the development of therapeutics for these currently incurable diseases.